Control system for powdered coal-fired burners



Oct. 29, 1957 e. R. ANDERSON 2,311,120

CONTROL SYSTEM FOR ROWDERED COAL-FIRED BURNERS Filed Aug.' 30, 1954 3Sheets-Sheet 1 IN V EN TOR.

GEORGE R. ANDERSON G. R. ANDERSON 2,811,120

Oct. 29, 1957 CONTROL SYSTEM FOR POWDERED COAL-FIRED BURNERS Filed Aug.30, 1954 3 Sheets-Sheet 2 INVENTOR. GEORGE A. Awe/e50 BY Z /s Oct. 29,1957 e. R. ANDERSON CONTROL" SYSTEM-FOR POWDERED COAL-FIRED BURNERS 3Sheets-Sheet 3 &

Filed Aug. 30, 1954 INVENTOR. GEORGE R. ANDERSON I es 3 CONTROL SYSTEMFor POWDERED COAL-FIRED BURNERS Application August 30, 1954, Serial No.452,778 9 Claims. ((31. 110 103 This invention relates to automaticcontrol systems for the regulation of combustion of fuels such aspowdered coal supplied by .a pulverizer, in accordance with the demandfor combustion as reflected by temperature, steam pressure, or othercondition which indicates the demand for combustion. While notnecessarily limited to the control of combustion in boiler furnaces, thesystem is particularly adapted to the control of the rate of supply ofpulverized coal 'by a pulverizer mill to the burners of the furnace inaccordance with the demand for steam.

An object of this invention is to provide a control system that willautomatically regulate the rate of supply of coal to a pulverizer millin accordance with the demand for combustion as reflected by a conditionsuch as temperature or steam pressure, and the rate of delivery ofpulverized coal to the burners of the combustion de- VICC.

Another object of this invention is to provide a con; trol system thatwill automatically regulate the rate of supply of coal to a pulverizermill in accordance witha predetermined relationship between boiler steampressure and the rate of delivery of pulverized coal to the burners ofthe boiler furnace.

Another object of the invention is to provide a system as above setforth having means for maintaining a substantially constant pressuredrop across an orifice in aduct leading from the mill classifier to anenhauster that supplies the pulverized coal to the burners.

A still further object of the invention is to provide a system as aboveset forth having means for controlling the rate of supply of secondary.air to the furnace or combustion device in accordance with apredetermined relationship between the condition to be regulated, forexample, temperature or steam pressure, or other condition reflectingthe demand for combustion, and the rate of supply of pulverized coal tothe burners of the furnace or combustion device.

And a still further object of the invention is to provide a system asabove set forth having means for controlling' the rate of supply ofsecondary air to the furn'ace in accordance with a predeterminedrelationship between the steam pressure generated by .the' boiler andthe rate of supply of pulverized coal to the burners of the boilerfurnace.

The above and other objects of the invention will be apparent to thoseof ordinary skill in the art to which the invention pertains from thefollowing description taken in conjunction with the accompanyingdrawings.

In the drawings:

Figure 1 is a more or less diagrammatic View of a steam boiler furnacesupplied with powdered coal as fuel;

Fig. 2 is a more or less diagrammatic view of a pulverizer mill and acontrol system for supplying pulverized coal to the burners of thefurnace shown in Fig. 1 at such a rate that the heat input to thefurnace is in ac cordance with the rate" at which steam is generated bythe furnace as measured by the steam pressure;

atent 2,311,120 Patented ea. 2s, rear Fig. 3 is a more or lessdiagrammatic view of a regulator included in Fig. 2 that responds to thepressure ofthe steam generated by the boiler and to the rate of deliveryof pulverized fuel to the burner for controlling the rate of supply ofraw or unpulverized coal to the pulverizer;

Fig. 4 is a more or less diagrammatic view of a regulater that measuresthe rate of delivery of pulverized coal to the furnace and develops acontrol force for regulating the rate of supply of secondary air to theburners of the furnace;

Fig. 5 is a view of a regulating device for maintaining a substantiallypressure drop across an orifice in a duct leading from the classifier ofthe pulverizer to an eirhauster which receives the coal from theclassifier and delivers it to the furnace burners;

Fig. 6 is a more or less diagrammatic view of a regulator for operatinga damper by which the pressure drop across the orifice in the ductleading from the mill classifier to the mill exhauster is maintainedsubstantially constant; and p Fig. 7 is a view of a power cylinderembodied in Figs. land 2 p The control system to be described infra,and-as illustrated in the drawings, is applicable to the control ofcombustion in steam boiler furnaces, and it is also applicable to theregulation of combustion in furnaces or other com' bustion devices wherecertain temperature conditions are to be maintained. In the one casetheprimary or moti v'a'ting force of the control system is the steampressure in the boiler, whereas, as in cases where temperature is to hethe motivating factor, the system responds to tem perature rather thansteam pressure. Whether the system is initiated by changes in steampressure or by changes in temperature, the control system operates tocontrol the supply of raw coal to a pulverizer mill in accordance withthe demand for combustion and to so regulate the secondary air that thecoal will be burned with efficiency While meeting the demands for heat;

In the following description the control system 'be described withparticular reference to its application to" a steam boiler furnace.

'In Fig. 1 of the drawings is shown a boiler furnace I having a steamdrum 2, a superheater 3 and a steam header 4 by means of which steam isdelivered to' steamconsumirig apparatus such as turbines, etc. Thefurnace is provided with burners 5 to which pulverized coal is deliveredby an exhauster 6 through a duct 7 to the burner 5. The exhauster 6exhausts pulverized coal from a pulverizer 8 (see Fig. 2) and deliversit through the duct 7 to the burners 5.

Secondary air is supplied to the furnace burners by means of a forceddraft fan 9 and a duct 10. The air delivered by the fan 9 is controlledby a damper 11in duct 10, the damper being actuated by a power cylinder12} The" power cylinder 12 is automatically controlled by the systemshown in Fig. 2. Power cylinder 12 may be of the type shown in DonaldsonPatent No. 2,044,936,

granted June 23, 1936, and as illustrated in Fig. 7 hereof.

The constr'u ction of power cylinder 12 is such that the stroke of itspiston for a given input signal pressure may be so controlled that thesecondary air will be propor tional to the weight of coal deliveredthrough duct 7 to the burners 5;

As schematically illustrated in Fig. l, a regulator 13 responds to thepressure of the steam generated by the' boiler. That pressure may besensed at the boiler drum or at the steam header 4, as shown. The steampressure in the header 4 is the initiating force of the control systemand the control system is so arranged that combustion will be regulatedto maintain the steam pressure substantially constant at the valuedesired.

Regulator 13 is provided with a pressure defiectable member 14 such as abellows disposed in a housing 15. The bellows divides the housing 15into pressure chambers 16 and 17. The pressure in header 4 iscommunicated to chamber 16 while chamber 17 is connected to theatmosphere. The bellows 14 actuates a beam 18 that extends through apressure flexible seal such as a bellows 19. Beam 18 is connected tobellows 14 by a push rod 20. Beam 18 actuates an escapement valve 21that is supplied with a pressure medium such as compressed air at asubstantially constant pressure by a supply pipe 22. The valve deliversa variable pressure to a sending pipe 23 in accordance with pressurechanges on bellows 14. The pressure in pipe 23 varies with the positionof the beam 18 and that pressure is supplied to a balancing device 24which includes a diaphragm 25. The pressure acts on diaphragm 25 whichin turn, acts through a push rod 26 on the beam 18. Therefore, if thepressure acting on bellows 14 is increasing, indicating that the steampressure is increasing, beam 18 tends to turn counterclockwise, therebyactuating the valve in a direction to increase the pressure in pipe 23.That pressure acting on diaphragm 25 exerts a balancing force on bellows14. Therefore, for every value of steam pressure there will be definitevalue of pressure established in the sending line 23. The function ofthe pressure in line 23 as utilized in the system shown in Fig. 2, is toadjust the control point of a steam pressure flow regulator, as will beexplained infra.

Fig. 2 illustrates schematically the pulverizer mill 8 and the controlsystem associated therewith. Mill 8 may be what is known as a bowl mill,to which coal is supplied by a feeder 26. The coal is fed to the millthrough a duct 27, the coal entering the mill through the bottomthereof. The feeder 26 is driven by a motor 28 preferably an adjustablespeed, direct current motor. The speed of the motor is controlled by afield rheostat 29 which is adjusted or positioned by means of a powercylinder 30. The position of the power cylinder 30 is controlled by asteam pressure-air flow regulator 31. The regulator 31 responds to thesending pressure in line 23 of regulator 13. Increasing pressures in thesteam header 4 above the regulated value to be maintained results inincreasing pressures being delivered to the power cylinder 30 with aresulting decrease in speed of the feeder motor 28 and a reduction inthe supply of coal to the pulverizer mill 8. More precisely stated, thepressures in sending line 23 of regulator 13 act on regulator 31 toestablish the particular set or regulating point thereof that is de-'termined by the steam pressure. In other words, if the steam pressure islower than it should be, the set point of the regulator 31 is increasedso that more coal will be delivered by the feeder 26 to mill 8 until theamount of coal delivered corresponds to the particular control pointestablished by regulator 13 on regulator 31. Conversely, if the steampressure is higher than the desired value, regulator 13 lowers thecontrol or set point of regulator 31 whereby the coal feeder motor 28 isdecreased in speed until the feed of coal is reduced to the valuerequired. Regulator 31 also responds to the pressure difference asmeasured between the outlet of the exhauster 6 and the pressure in thecombustion chamber of the furnace as measured at a point at the sameelevation as the burners. The pressure point or connection to theexhauster 6 may be designated the P1 connection and the pressureconnection to the furnace at the burner level may be designated the P2connection. Since the regulator 31 responds to the pressure in pipe 23which is a function of the rate of steam flow, and to the differencebetween the pressures at connection points P1 and P2, the controlpressure delivered to power cylinder 30 through line 33 will be afunction of the steam pressure and the rate at which fuel is deliveredto the burners of the furnace.

The coal as pulverized in mill 8, is carried upwardly by the air flowinduced by the exhauster fan 6 into a classifier 34. The coal isconveyed from the classifier 34 through a duct 35 to the intake of theexhauster 6. The exhauster 6 and the pulverizer mill may be driven by amotor 37. In the duct 35 is an orifice 38. The pressure drop across thatorifice is measured by a regulator 39 which, in turn, controls a damperoperator 40. Damper operator 40 as shown, is connected to a damper 41 inthe pipe 36 down stream of orifice 38. Regulator 39 operates to soposition damper positioner 40 and damper 41 that the pressure dropacross orifice 38 will be maintained substantially constant at a presetvalue.

As stated supra, the secondary air is supplied by fan 9 through duct 10.The secondary air is regulated by and in accordance with the rate atwhich pulverized coal is delivered through duct 7 to the furnaceburners. In order to so regulate the rate of supply of secondary air aregulator 42 is provided. The regulator 42 responds to the pressure dropacross the pressure connections P1 and P2 and sends out a controlimpulse that causes the power operator 12 to so position the damper 11that the secondary air will be in the correct relationship to the supplyof pulverized coal to the burner. The pressure drop P1P2 is a linearfunction of the weight of coal carried in suspension in the primary airflowing in duct 7. Regulator 42 is adjusted to zero output pressure whenthe primary air contains no coal. When so adjusted, the control impulsefrom regulator 42 will vary from a minimum gauge value, for example,Zero, to a maximum value corresponding to the value of the supplypressure when the primary air contains more or less coal as required.

In the operation of a pulverizing mill such as the one indicated in Fig.2, hot or heated air may be supplied to the suction side of the mill forpreheating the coal. As shown, the heated air enters at the bottom ofthe mill through a duct 44. A damper 45 which may be manually operatedor adjusted for regulating the amount of heated air supplied, isprovided. Damper 45 as shown, is operated manually by a bell crank 46connected by a cable 47 operating over pulleys 48. The bell crank may bemanually positioned by means of a screw 49 and handwheel 50. On thescrew is a traveling nut 51 connected to the crank .46.

In order to further regulate the air supply to the mill and to temperthe heated air, a counter-balanced damper 52 is provided. Damper 52 ismounted on a shaft 53 to which a lever arm 54 is connected andcounter-weighted by a weight 55. The weight 55 is so adjusted that thedamper 52 will take a position depending upon the suction on the mill.If the suction in the mill increases, damper 52 automatically swingsopen to allow more air to flow into the mill. If the suction decreases,the damper swings towards a more closed position.

The details of construction of regulator 31 are shown more particularlyin Fig. 3. As there illustrated, the regulator includes a parted housing57 at the part line of which the marginal edge of a diaphragm 58 isclamped. The diaphragm 58 divides the housing into pressure chambers 59and 60. The diaphragm is provided with a push rod 61 having a knife edge62 that bears against the upperside of a lever 63. The lever 63 actuatesan escapement valve 64 having a valve body 65 in which is a valve 66that is connected by a stem 67 to the lever' 63. The valve 66 hascomically tapered ends that control the inlet port 68 and the exhaustport 69 in the valve body. Air pressure at a substantially constantpressure is supplied to the inlet 70 of the valve body. The valve bodyis provided with an outlet port 71 that is connected to sending line 33leading to the power cylinder 30.

The regulator 31 is provided with a dash-pot 72 that stabilizes theregulator. The dash-pot includes a cylinder 73 which is open at itsupper end and connected at its lower end to the interior of a bellows 74mounted in a housing 75. The bellows works against a compression spring76. The dash-pot includes a piston 77 that is connected by a spring 78to the diaphragm 58. A sealing diaphragm 79 seals the opening throughwhich the connection between the diaphragm and spring 78 extends.Similarly, there is a sealing diaphragm 80 that seals the openingthrough which the push rod 61 extends.

The cylinder 73 and bellows 74 contain fluid such as oil having asubstantially constant viscosity. The oil level rises to a point abovethe piston 77. A bypass 78 connects the space above and below piston 77,and a needle valve 79 is provided in the by-pass to regulate the rate ofinterchange of oil between the space above the piston and that below it.The pressure delivered to the sending line 33 is communicated to thehousing 75 which compresses the bellows in proportion to the pressure,the spring. 76 causing the bellows to take a definite deflection foreach value of pressure. The regulator 31 regulates to a set point thatis governed by the sending pressure developed in line 23 by regulator13. The sending pressure is delivered to a chamber 82 of regulator 31,having therein a diaphragm 83. The diaphragm works against a compressionspring 84. Motion of the diaphragm is communicated to lever 63 by a pushrod 85, but that motion is resisted by a spring 85' that urges the leverto a position at which the output pressure in line 33' would be at aminimum value.

Chamber S9 of regulator 31 is connected to the pressure connection P1 inthe exhauster 6 and chamber 60 is connected to the pressure connectionP2 in the furnace chamber at a point located preferably at the samelevel as the burners. Therefore, the difference in pressure at theconnections P1 and P2 will urge the diaphragm 58- downwardly. Thepressure in chamber 82 acts to tilt lever 63 clockwise and in the samedirection as it would be turned by an increase in pressure difierenceacting on diaphragm 58. Therefore, for every loading pressure applied tochamber 82, the regulator 64 will establish such a pressure in sendingline 33 that the rheostat 29 would be adjusted to a position in whichthe raw coal is delivered to the mill at the rate required by the steampressure air flow relationship.

The stabilizing action of dash-pot 72 on regulator 31 is as follows: Ifan increase in pressure on diaphragm or bellows 74 results fromdeflection of diaphragm 58, that pressure acting on the piston throughspring 78 will impose a loading, on diaphragm 58 that resists suddendeflections of the diaphragm in response to changes in the pressureacting in chambers 59 and 60. The resisting force is dissipated as oilflows through the needle valve 79. On decreasing pressures the reverseaction takes place.

From the foregoing, it will be seen that regulator 31 so controlsthrough regulator 30 and rheostat 29, the speed of operation of motor28, that feeder 26 will deliver raw coal to the mill 8 at the raterequired by the combined effects of steam pressure and the rate ofdelivery of pulverized coal to the furnace burners.

Regulator 42 is illustrated more in detail in Fig. 4. As there shown,the regulator comprises a parted housing 90 which clamps the marginaledge of a diaphragm 91 at the part line of the housing to provideopposed chambers 91a and 91b. The diaphragm operates a beam 92 through apush rod 93 and a knife edge 94 that acts downwardly on the beam. Thebeam is provided with a stationary fulcrum 95. The point where the pushrod 93 passes out of the housing is sealed by a flexible dia phragm 96.The lever 92 actuates an escapement valve 64' which is similar inconstruction and operation to valve 64 shown and described in connectionwith Fig. 3. The inlet of valve 64' is supplied with compressed air atsubstantially constant pressure and it delivers a variable pressure to asending line 92. The sending line 92' is connected to the pilot valveoperator 94 of power cylinder 12.. Pressure chamber 91a is connected tothe pressure connection P1 of the exhauster 6 and chamber 915 to thefurnace pressure connection P2. Thus the diaphragm 91 responds to thedifference between the t t 6 pressures at the connections P1 and P2;That pressure difierence is a direct measure of the amountofcoal carriedthrough the duct 7 to the burners.

Power cylinder 12 and the pilot valve operator 94'may actuated by adiaphragm 97d to which the signal pressure is supplied by pipe 92 ofregulator 42. The pressure works against a spring 97e carried in asocket 977. Socket 971 is carriedby one arm of a bell crank 97g, theother arm of which has a follower roller'97h' that rides on a cam orcompensating bar 97i. Bar 97i is' secured 'to'a' frame 97 attached tothe piston rod 97k of the power cylinder 12. As the piston rod 97k moveseither upwardly or downwardly, the bar 971 so adjusts the tension inspring 97e that the pilot valve is returned to neutral when the pistonhas moved a certain distance in either direction in response to aparticular pressure in pipe 92'. 'By properly shaping the bar 971', thethrow of'crank 97g can beincreased or decreased at different portions ofthe stroke of power cylinder piston so that the damper 111will be'positioned to cause the secondary air to be proportional to the pressureddifference P1P2. as measured by regulator 42. Consequently, the rate offlow of secondary air-will be proportional to the weight of coal carriedby the primary air in duct 7 to the burners. i In order that theregulator 42 will have a definite send-'- ing pressure in line 92' forevery value of pressure diflerence on diaphragm 91, the regulator isprovided with a diaphragm housing 98 having therein a diaphragm 99 thatacts through a push rod 100 on the beam 92, and exerts a force opposingthe force of diaphragm 91 on the beam. As shown, thediaphragm 99 actsagainst a' compression spring 101 so that the diaphragm'will take ajdefinite deflection for every value of sending pressure in line 92'.Since regulator 42 develops a sending pressure in line 92' that isproportional to the rate of flow of coalto the burners, the secondaryair supplied by forced draft fan 9 through duct 10 to the furnace willbe proportionah to the rate at which coal is delivered to theburners.

Regulator 42 may be provided with an adjustable ten 7 sion spring 104whereby the zero'of the regulator can be suppressed more or less asrequired. That is to say, that'- the spring can be so adjusted that theoutput pressure of valve 64 will be zero gauge when there is nocoal'intheprimary air flowing through duct 7 to the burners. When so adjusted,the output pressure of valve 64' will increase from zero gauge to amaximum value as the amount of 7 coal carried in suspension in duct 7increases from zero to full capacity. As the pressure difference P1-P2is lin-- early proportional to the coal weight suspended in the primaryair, the regulator 42 will transmit a pressure out put that varies fromzero gauge to the maximum of its range on the basis of the presence ofcoal in the primary air and the density of the coal in that air.

The regulator 39 of the control system is illustrated schematically inFig. 5. The regulator comprises atwopart housing 106 having therein adiaphragm 107 whose marginal edge is clamped between the two. parts ofthe.

housing at the part line thereof. The diaphragm 107 thus providespressure chambers 108 and 109. Pressurechamber 108 is connected by apipe 110 to the up stream. side of orifice 38 in duct 35, while chamber109 is con.-. nected by a pipe 111 to the down stream side of that Thediaphragm is connected by a push rod 112 and a.

knife edge 113 to a beam 114 that is mounted at one end sure through aline 116 to the power operator 40 that adjusts the position of damper 41so as to maintain a substantially constant pressure drop across theorifice 38.

Beam 114 is connected to an adjustable tension spring 118 so that thedead weight of the diaphragm, the strut or push rod 112, and the knifeedge 113 may be balanced, thereby causing the pressure acting on thediaphragm 107 to effect a motion of beam 114 that is proportional to thepressure.

Since regulator 39 responds to changes in the pressure difference acrossorifice 38 and causes the power operator 40 to adjust damper 41 inaccordance with those changes, the pressure drop across the orifice 38will be maintained at a substantially constant value. The tension spring118 may also be used to establish the set point of the regulator 39, theset point being the pressure difference to be maintained across theorifice 38. V

In case necessity requires, the control system may be operated manuallyby means of a hand sender 120 by means of which the pressure in line 33leading to the regulator 30 may be manually adjusted and a hand sender121 by means of which the pressure delivered to the power operator 40may be adjusted manually. Where the control is to be effected manually,valves 122 and 123 are provided for disconnecting the sending line 33leading from regulator 31 to the valve 122 and shutting off the pressureleading from the escapement valve of regulator 39 to the operator 40. t

The power operator 40 of Fig. 2 is illustrated more or lessschematically in Fig. 6, and comprises a two-part housing 125 having adiaphragm 126 therein, the marginal edges of which are clamped betweenthe housing parts at the part line thereof. The diaphragm is urgeddownwardly by an adjustable tension spring 127. Pressure delivered byregulator 30 to the operator 40 is delivered into chamber 128. Thatpressure acts upwardly on the diaphragm 126. Diaphragm 126 is connectedby a. push rod 129 to a lever 130 which is pivoted at one end as at 131.The opposite end of the lever is connected by a link 132 to a lever arm133 connected to the shaft 134 of damper 41. For every value of pressuredelivered to chamber 128, lever 130 will take a definite position andtherefore actuate damper 41 to a definite position. That position willdepend upon the deviation of the pressure drop across orifice 38 fromthe preselected value.

From the foregoing description it will be seen that a regulating systemis provided whereby raw coal is fed to a pulverizer mill at such a ratethat the steam pressure in the boiler is maintained substantiallyconstant. It will also be seen that the system includes a regulator forautomatically adjusting the secondary air in accordance with the totalamount of coal delivered to the burners.

Since pulverized coal carried in a stream of air will cause a pressuredrop between the pressure connections P1 and P2 that is directlyproportional to the weight of coal flowing through the duct 7 per unitof time, the provision for maintaining the constant pressure drop acrossthe orifice 38 will cause the pressure drop between the pressureconnections P1 and P2 to be a true and accurate measure of the totalweight of coal delivered to the burners per unit of time.

The foregoing description has dealt with the system as applicable to asteam boiler. If the system is to be used for regulating combustion tomaintain a given temperature in a given combustion space or the like, athermostat can be substituted for regulator 13. Such a thermostat wouldbe equipped with an escapement valve for delivering a signal toregulator 31 to adjust the set point of that regulator in accordancewith the departure of the regulated temperature from the predeterminedvalue. If the temperature is above the regulated value the set point ofregulator 31 will be modified by the pressure loading rom the thermostatto decrease the combustion rate if the temperature is below theregulated value, the regulator 31 will be adjusted by the thermostatimpulse to a set point that will require a higher rate of combus. tionuntil the temperature condition is satisfiedby the combustion rate. Athermostat suitable for substitution of the regulator 13 may be of thetype shown ingFig. 5 of A. A. Markson Patent No. 2,497,783, grantedFebruary 14, 1950. The thermostat shown in Fig.5 of that patent has anescapement valve with an outlet port 1'7. through which pressures ofvarying magnitude are transmitted, depending upon the temperature towhich the thermostat responds. That pressure would bev communicated tothe diaphragm 83 of regulator 31. j

Having thus described the invention, it will he appar-' ent to those ofordinary skill in the art to which the invention pertains, thatmodifications and changes may be made in the illustrated embodimentswithout departing from either the spirit or the scope of the invention.Therefore, what is claimed as new and desired to be secured by LettersPatent is:

l. The combination with a steam boiler furnace having powdered coalburners provided with means for sup plying secondary air thereto, apulverizer mill, a coal feeder for the mill, a motor for driving thecoal feeder, the motor having means for adjusting the speed thereof,said powdered coal mill having a classifier, an exhauster and a ductfrom the classifier to the exhauster, and a discharge duct for conveyingair and coal suspended in said air from the exhauster to the burners,the duct from the classifier to the exhauster being provided with anorifice, of a control system therefor comprising a first regulatorresponsive to the pressure drop across the orifice for developing acontrol force, the magnitude of which varies by and in accordance withsaid pressure drop, damper means in the duct from the classifier to theexhauster, an operator controlled by the control force of the firstregulator for so adjusting the damper means as to maintain the pressuredrop across the said orifice substantially constant, a second regulatorresponsive to the boiler steam pressure and to the pressure drop fromthe exhauster to the burners for developing a control force that variesby and in accordance with the combined effect of said steam pressure andpressure drop, an operator responsive to the control force of the secondregulator for actuating the speed adjusting means for the coal feedmotor, whereby raw coal is delivered to the mill in accordance with theresponse of the second regulator to the steam pressure and the coalladen air flow pressure drop, and a third regulator responsive to therate of flow of coal laden air through the duct leading from theexhauster to the burners for controlling the secondary air supply meanswhereby the supply of coal to the burners and the supply of secondaryair are caused to bear a predetermined relationship to the boiler steampressure.

2. The combination with a boiler furnace provided with powdered coalburners and secondary air supply means therefor, a coal pulverizer, acoal feeder for the mill, an adjustable speed motor for driving thesame, said motor being provided with means for adjusting the speedthereof, an exhauster for conveying powdered coal from the mill to thefurnace burners and means between the mill and the exhauster fordeveloping a pressure drop that varies in accordance with the fiow ofair and coal to the exhauster and regulator means for adjusting thesecondary air supply of a control system therefor comprising a firstregulator responsive to the boiler steam pressure for developing acontrol impulse whose magnitude varies by and in accordance withvariations in the steam pressure, a second regulator responsive to therate at which coal by weight as suspended in the carrier air from saidexhauster, is delivered to the furnace, said second regulator havingmeans responsive to the control impulse of the first regulator and tothe rate of coal delivery to the burners, whereby said second regulatordevelops a control force that is proportional to the boiler steampressure control force and to the coal weight feed rate for controllingthe speed of the coal feeder motor,

a third regulator responsive to the flow of air and the weight of coalsuspended therein as delivered to the furnace burners for developing acontrol force for so adjusting the secondary air supply regulating meansthat the rate of flow of secondary air to the burners is by and inaccordance with said air and the coal flow to the burners, means fordeveloping a pressure drop between the coal pulverizer and the exhausterthat varies by and in accordance with the air flow from the mill to theexhauster, and means responsive to said pressuredrop for so regulatingsaid flow to the exhauster that the pressure drop is maintained at asubstantially constant predetermined value.

3. A control system in accordance with claim 1 in which the thirdregulator is provided with means whereby the control impulse developedthereby may be adjusted relative to the control impulse developed bysaid second regulator.

4. A control system in accordance with claim 2 characterized by the factthat means are provided in the third regulator for adjusting the controlimpulse thereof relative to the control impulse developed by the secondregulator that controls the speed of the coal feeder motor.

5. The combination with powdered coal burners provided with a source ofsupply of secondary air and means for regulating the supply of secondaryair, a pulverizer mill for supplying coal to the burners, the mill beingprovided with a classifier, an exhauster, a first duct leading from theclassifier to the exhauster, and having an orifice in the same, and asecond duct leading from the exhauster to the burners, of a controlsystem for the same comprising a regulator responsive to the pressuredrop across said orifice for developing a control force the magnitude ofwhich varies by and in accordance with said pressure drop, means in thefirst duct for adjusting the flow of coal laden air therethrough, andmeans operated by the control force of said regulator for so actuatingsaid flow adjusting means that the pressure drop across said orifice ismaintained substantially constant, and means responsive to the pressuredrop through the second duct for developing a control force whosemagnitude varies by and in accordance with the weight of coal carried byair therethrough, the control force of said pressure drop responsivemeans actuating the secondary air supply regulating means.

6. A control system according to claim 5 in which the means responsiveto the weight of coal flowing to the burners responds to the pressuredrop as measured from the outlet of the exhauster to the burners.

7. The combination with a powdered coal combustion device for burningsuch coal in accordance with a condition to be maintained, thecombustion device being provided with a pulverizer mill, means fordelivering raw coal to the mill at adjustable rates, said mill having aclassifier, an exhauster and a duct leading from the classifier to theexhauster, an orifice in said classifier duct, a second duct from theexhauster to the burners, and means for supplying secondary air to theburners of a control system therefor comprising means responsive to thecondition to be controlled for developing a control force whosemagnitude varies by and in accordance with changes in said condition,means responsive to the flow of air and coal from the exhauster to theburners and to said condition responsive control force for adjusting thecoal feed means to increase coal feed as the condition responsivecontrol force decreases below a predetermined value and to decrease thesame as the condition responsive control force increases above saidvalue, means responsive to the pressure drop across said classifier ductorifice for maintaining said drop substantially constant, and meansresponsive to the rate of flow of air containing coal in suspension, tothe burners for adjusting the secondary air supplying means by and inaccordance with the weight of coal delivered in the exhauster air to theburners.

8. The combination with powdered coal burners provided with a pulverizermill, means for supplying raw coal to the mill at regulatable rates, anexhauster, a classifier duct connecting the mill classifier to theintake of the eXhauster through which powdered coal is withdrawn fromthe mill with air constituting primary air for the burners, a ductleading from the exhauster to the burners, an orifice in the classifierduct and means for supplying regulatable amounts of secondary air to theburners, of a control system therefor comprising means responsive to thepressure drop across the orifice in the classifier duct for developing acontrol force whose magnitude varies by and in accordance with saiddrop, damper means in said duct and an operator therefor having meansresponsive to said control force for causing the same to so actuate thedamper means that the flow through the classifier duct is controlled tomaintain a substantially constant pressure drop across said orifice, andmeans responsive to a condition to be controlled and to the pressuredrop from the exhauster outlet to said burners for developing a controlforce whose magnitude varies by and in accordance with the same, andmeans responsive to said control force for s0 regulating the coalfeeding means as to maintain said condition at a preselected value,whereby changes in the feed of coal to the mill are effectedsubstantially instantaneously with changes in weight of coal carried tothe burners.

9. A system as in claim 8 having a regulating means substantiallyinstantaneously responsive to changes in the pressure drop from theburners to the exhauster as affected by changes in the rate at whichcoal is carried to the burners by the primary air, for developing acontrol force whose magnitude varies by and in accordance with the sameregulating the secondary air supply means in accordance with the rate atwhich coal is delivered to the burners.

References Cited in the file of this patent UNITED STATES PATENTS

